Phase pre-emphasis for a serial data transmitter
View Patent ↗Apparatus and methods apply pre-emphasis to the phase rather of a signal than to the amplitude of a single. This approach can provide superior pre-emphasis performance than the conventional amplitude pre-emphasis techniques in certain situations, such as when a non-linear slicer is present in the signal path. For example, electrical-to-optical (E/O) and optical-to-electrical (O/E) converters can effectively slice a signal.
1. An apparatus for phase pre-emphasis, the apparatus comprising:
a pattern detector configured to detect one or more patterns in data to be transmitted in a serial data signal;
a modulator configured to stretch a pulse width of one or more bits of the one or more detected patterns in the serial data signal, wherein the modulator is configured to modify a clock signal to generate the modified clock signal, wherein the modified clock signal has a wider clock pulse than the clock signal for the one or more bits of the one or more detected patterns, wherein the clock signal and the modified clock signal are half rate, the modulator further comprising:
a clock driver wherein an output of the clock driver is the clock signal;
a pulse width modulator circuit having an output in parallel with the output of the clock driver such that when enabled, the output of the pulse width modulator circuit is in contention with the output of the clock driver;
a control circuit configured to enable the output of the pulse width modulator circuit for an emphasis period that encompasses a half clock cycle to be stretched, at least a portion of a preceding half cycle, and at least a portion of a subsequent half cycle; and
a buffer circuit with an input coupled to both the output of the clock drive and the output of the pulse width modulator circuit; and
a serializer configured to convert the data from parallel form to serial form, wherein the serializer is configured to receive a modified clock signal as an input for timing of the serial data signal.
2. The apparatus of claim 1 ,
wherein a pattern of the one or more patterns comprises an isolated bit of a first logic state surrounded by two or more preceding bits of a second logic state and two or more subsequent bits of the second state, wherein the second logic state is opposite to the first logic state, wherein the modulator if further configured to stretch the pulse width of the isolated bit relative to surrounding bits.
3. The apparatus of claim 1 , wherein the emphasis period is 3 half-cycles long.
4. The apparatus of claim 1 , wherein the pulse width modulator circuit comprises a 3-stateable gate.
5. The apparatus of claim 1 , wherein the pulse width modulator circuit comprises an open-drain circuit.
6. The apparatus of claim 1 , further comprising one or more shift registers configured to hold parallel data to be converted into the serial data signal, wherein the one or more shift registers are configured to output serial data in response to the modified clock signal.
7. The apparatus of claim 1 , wherein the modulator is configured to stretch the pulse width by modulation of a duty cycle of a clock signal used for timing the serial data signal.
8. The apparatus of claim 1 , wherein the modulator is configured to stretch the pulse width such that after being sent through a transmission channel, the stretched pulse width is received with an undistorted pulse width.
9. An apparatus for phase pre-emphasis, the apparatus comprising:
means for detecting one or more patterns in data to be transmitted in a serial data signal;
means for selectively stretching a pulse width of one or more bits of the one or more detected patterns in the serial data signal by:
modifying a clock signal to generate a modified clock signal, wherein the modified clock signal has a wider clock pulse than the clock signal for the one or more bits of the one or more detected patterns and wherein the clock signal is a half-rate output of a clock driver;
using the modified clock signal to time the sequence of bits of the serial data signal; and
selectively stretching the pulse width of the modified clock signal by enabling an output of a pulse width modulator circuit that is in parallel with the clock driver such that the output of the pulse width modulator circuit is in contention with the output of the clock driver, wherein the output of the pulse width modulator circuit is enabled for an emphasis period that encompasses a half clock cycle to be stretched, at least a portion of a preceding half cycle, and at least a portion of a subsequent half cycle.
10. The apparatus of claim 9 ,
wherein a pattern of the one or more patterns comprises an isolated bit of a first logic state surrounded by two or more preceding bits of a second logic state and two or more subsequent bits of the second state, wherein the second logic state is opposite to the first logic state, the apparatus further comprising means for selectively stretching the pulse width of the isolated bit relative to pulse widths for surrounding bits.
11. A method for phase pre-emphasis, the method comprising:
detecting one or more patterns in data to be transmitted in a serial data signal; and
selectively stretching a pulse width of one or more bits of the one or more detected patterns in the serial data signal and selectively stretching the pulse width by:
modifying a clock signal to generate a modified clock signal, wherein the modified clock signal has a wider clock pulse than the clock signal for the one or more bits of the one or more detected patterns and wherein the clock signal is at half-rate output of a clock driver;
using the modified clock signal to time the sequence of bits of the serial data signal; and
selectively stretching the pulse width of the modified clock signal by enabling a pulse width modulator circuit that is in parallel with the clock driver such that the output of the pulse width modulator circuit is in contention with the output of the clock driver, wherein the pulse width modulator circuit is enabled for an emphasis period that encompasses a half clock cycle to be stretched, at least a portion of a preceding half cycle, and at least a portion of a subsequent half cycle.
12. The method of claim 11 ,
wherein a pattern of the one or more patterns comprises an isolated bit of a first logic state surrounded by two or more preceding bits of a second logic state and two or more subsequent bits of the second state, wherein the second logic state is opposite to the first logic state, the method further comprising selectively stretching the pulse width of the isolated bit relative to surrounding bits.
13. The method of claim 11 , wherein the emphasis period is 3 half-cycles long.
14. The method of claim 11 , wherein the pulse width modulator circuit comprises a 3-stateable gate.
15. The method of claim 11 , wherein the pulse width modulator circuit comprises an open-drain circuit.
16. The method of claim 11 , wherein selectively stretching the pulse width comprises modifying a duty cycle of a clock signal used for timing the serial data signal.
17. The method of claim 11 , further comprising selectively stretching the pulse width such that after being sent through a transmission channel, the stretched pulse width is received with an undistorted pulse width.
18. The method of claim 11 , further comprising:
receiving the data in parallel form; and
converting the data to generate the serial data signal.